It is common practice to label blow molded plastic articles in order to provide information to consumers of the articles, and in an aesthetically pleasing manner. The labels provide product identification information, and also may contain indicia promoting the product. The common commercial method for such labeling is to use a polyvinyl chloride label substrate having adhesive on one face which is covered by a release sheet. The plastic surface may be constructed of various curvatures depending on the shape and diameter of the mold. Plastic articles are produced by coating a mold with a release agent, and then injecting hot plastic (in liquid form) into the blow mold to create a molded plastic article (e.g. a planter, refuse container, dish tray, or almost an infinite variety of other types of articles). Once the product is molded it is removed from the blow molding equipment, typically at a temperature between about 160-180.degree. F. The plastic product identification label is then hand applied to the finished unit while the article is still hot (e.g. at a temperature up to 160.degree. F.). The article then cools down, causing the plastic material to contract. The pressure sensitive label must conform properly to the product during the cooling process and remain adhered with no visible flaws (such as lifted edges, air bubbles, or puckering). While this technique is effective, polyvinyl chloride is not very environmentally friendly, so that a more acceptable alternative is needed.
U.S. Pat. No. 4,729,864 teaches a method of forming plastic containers that have labels that may be made out of paper rather than plastic. In this method the paper label has a heat activated adhesive and is placed inside the blow mold itself. The heat from a parison, and the pressure generated by the blow medium, binds the label onto the blown container sidewall. However, unless the moisture of the label is controlled, the rate of shrinkage of the label is different than the plastic sidewall of the blow molded article so that the label does not adhere properly. Therefore, it is necessary to use a label that has been specifically acted on so that it has a moisture level of between about 6-8%. This procedure is complicated, requiring integration of the label with the blow molding process rather than applying the label to a final product.
U.S. Pat. No. 5,238,720 shows another method of labeling a molded article. However, here too the label is added to the mold, the label having a two layer construction including a base portion molded to the actual blow molded article, with a removable second layer. The second layer may comprise a latex impregnated paper.
According to the present invention, a method of labeling a blow molded plastic article, a label for application to a blow molded plastic article, and a method of making and using a label are provided which allow the effective labeling of blow molded articles in an environmentally friendly manner, that does not require placing the label in the mold. Rather, the label according to the present invention, which is of paper stock, may be applied directly to a surface of the blow molded article, e.g. while it is still hot, yet when the article with label cools the label conforms to the surface of the article without visible flaws (i.e. without lifted edges, air bubbles or puckering).
According to one aspect of the present invention a label, ideally suited for application to a blow molded plastic article, is provided. The label comprises the following components: A highly calendered paper stock label substrate having first and second faces. Indicia imaged on the first face. An adhesive release coat on the first face. And a pressure sensitive adhesive on the second face.
The paper stock label substrate preferably has a thickness of between about 2-4 mil, e.g. about 3 mil. Also, the label substrate preferably has a moisture content of between about 6-8%, the adhesive release coat and the pressure sensitive adhesive sealing the moisture within the paper stock label substrate so that even if the label is applied hot to the article it has a suitable rate of shrinkage so that visible flaws do not form in the label in the final label product. The adhesive may be a permanent acrylic adhesive, while the release coat is a silicone release coat. The label may be in roll form with a plurality of other labels, the adhesive from one contacting the release coat of others, and the release coat may be provided over the imaged indicia. Imaging may also be provided on the second face of the label stock, covered by the pressure sensitive adhesive, particularly in situations where the article is transparent or translucent so that the indicia on the second face may be read from the exterior of the article even with the label applied to the article.
According to another aspect of the present invention, a method of labeling a blow molded plastic article using a paper label having a first printed face having an adhesive release coating, and a second face having pressure sensitive adhesive, is provided. The method comprises the following steps: (a) Blow molding, in a mold, an article having a first surface for receiving a label by introducing heated plastic into the mold. (b) Removing the article from the mold while the article is still in heated condition. (c) Applying the paper label to the article while the article is still in heated condition with the pressure sensitive adhesive contacting the first surface of the article, and the release coated first face of the label facing away from the article. And (d) cooling the article, so that the label conforms to the first surface of the article without visible flaws.
Steps (b) and (c) are preferably practiced with the "heated condition" at a temperature of over 120.degree. F. (e.g. between 150-160.degree. F.). The label preferably is as described above, with permanent acrylic adhesive applied directly to the article first face, and with the paper stock having a moisture content of between about 6-8% which is sealed therein by the release coat and the adhesive.
According to another aspect of the present invention a method of making and using a label is provided comprising the following steps: (a) Highly calendering paper stock to form a paper label substrate having first and second faces. (b) Imaging a first face of the substrate. (c) Coating the first face of the substrate with adhesive release material. (d) Coating the second face of the substrate with pressure sensitive adhesive. And (e) applying the pressure sensitive adhesive to a first surface of an article so that the adhesive sticks to the first surface without visible flaws.
Step (e) may be practiced by applying the pressure sensitive adhesive to a blow molded plastic material while the article has a temperature of above 120.degree. F., and the label may have the construction as described above. Steps (a) through (e) may be practiced sequentially, although other sequences are also possible, such as applying the adhesive release material before imaging, or applying the pressure sensitive adhesive simultaneously with or before application of the release coat, etc.
It is a primary object of the present invention to provide for the effective labeling of blow molded plastic articles, the labels when applied to the articles having now visible flaws, and being environmentally friendly. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.